转录因子IRX3调节白色脂肪棕色化参与肥胖发生的机制研究

FTO, a susceptible gene for obesity was identified and confirmed in diverse populations. IRX3 was recently reported as the effector of the FTO variants. However, the role of IRX3 in obesity and the molecular mechanism is not clear. To our knowledge, there is as yet no study to target sequencing IRX3 in human cohort of obese participants. we sequenced the whole coding exons of human IRX3 gene in 861 young obese participants and 916 healthy lean controls. Rare IRX3 variants were identified, with a significant enrichment in obese subjects. Moreover, IRX3 promotes the browning of white adipocytes in mouse models and in vitro. Based on the previous results, we hypothesized that IRX3 might compete with SMAD3 and binding to the promoter of UCP1, then recruit PGC1ɑ to increase the transcriptional activity of UCP1. By inducing the browning of white adipocytes, IRX3 over-expression were protected against obesity. In order to further explore the function of IRX3, we will sequence the whole coding exons of human IRX3 in families with rare heterozygous IRX3 variants to study the genetic association. Further in this study，we will establish the brown adipose tissue specific IRX3 transgenic mouse model. By using these mouse models and collecting families with rare heterozygous IRX3 variants, we will demonstrate the significant role and underlying mechanism of IRX3/SMAD3/ PGC1ɑ pathway in the function of white to brown switch and body weight regulation in vivo and vitro. Altogether, our study will provide a new idea for the pathogenesis and therapy of obesity.

FTO基因在肥胖遗传学中占据极其重要地位。而近期研究表明，FTO基因肥胖关联位点的真正效应基因是IRX3。然而，IRX3基因本身的变异是否导致人类肥胖及其具体机制尚不清楚。我们前期对861例肥胖患者及916例对照人群进行IRX3外显子测序，首次发现IRX3的低频变异位点在肥胖患者中富集；动物模型及体外实验证明IRX3促进白色脂肪棕色化。基于前期研究结果，我们提出科学假说：IRX3与SMAD3竞争性结合到UCP1启动子区，并招募PGC1ɑ，促进UCP1表达，从而促进白色脂肪棕色化抵抗肥胖发生。本研究拟在前期工作的基础上收集携带IRX3稀有变异位点的三代家系，分析IRX3变异与肥胖的连锁遗传关系。其次，本研究拟构建UCP1cre-IRX3转基因小鼠，从体内外水平探讨IRX3通过SMAD3/PGC1ɑ信号通路调节白色脂肪棕色化参与肥胖发生的机制。上述问题的阐明将为肥胖的治疗提供新的思路。

研究背景：IRX3基因在能量消耗中的作用仍不清楚。本研究通过构建条件性过表达动物模型， 阐明在体内过表达人源性IRX3对棕/米色脂肪组织能量代谢及产热活动的影响。.研究内容：我们构建了棕色/米色脂肪特异性hIRX3过表达小鼠（Rosa26hIRX3;Ucp1-Cre）。利用棕色化模型冷冻和CL316,243 刺激模型观察白色脂肪组织棕色化的改变，同时测量小鼠体重、脂肪组织重量、瘦组织重量和能量消耗，并分析脂肪组织形态学和产热相关基因改变。进一步，我们分离了IRX3过表达小鼠的原代脂肪前体细胞体外诱导分化，观察脂肪细胞的棕色化能力。之后我们用RNA测序的方法检测产热相关基因的改变。.研究结果：结果发现，棕色/米色脂肪组织过表达hIRX3的小鼠较对照小鼠体重下降，体脂减少，能量消耗增加。冷冻模型和CL316,243刺激模型结果显示棕色/米色脂肪组织过表达 hIRX3的小鼠脂肪组织Ucp1表达明显增加。与此同时，体外对原代脂肪前体细胞进行诱导分化结果显示， hIRX3过表达的脂肪前体细胞诱导分化后其 Ucp1表达更高，并且氧耗增加。RNA测序结果显示，棕色脂肪细胞IRX3过表达促进棕色脂肪细胞的分化。.结论：本研究表明，体内过表达hIRX3可以增强棕色及米色脂肪组织Ucp1的表达和产热作用，降低脂肪组织含量。这为我们更全面地理解IRX3在能量平衡和肥胖发生中的作用提供了更多的证据。